In ArchiCAD 21, several long-lived 2D Objects were removed from the ArchiCAD Library, which were very useful for detailing consistently. These include wood trim profiles, break lines, brackets and hold-downs, brick coursing, a column marker, and section/detail markers for use in the Detail/Worksheet windows. Most of these included the prefix "DET", and were part of the fondly remembered MSA Detailer system.
Please bring these back! I've never had a problem with too many objects. They should never delete a library part unless it specifically conflicts with a new feature.
These can be retrieved by loading Migration Libraries, but that's a poor substitute, and only works if objects are already placed in a Project.
More discussion is here: http://archicad-talk.graphisoft.com/viewtopic.php?p=268657&highlight=detail+objects#268657
I was notified that there is a "placeable" migration library 20 with the missing parts available on the ArchiPlus site. If you are on subscription, you have access to it. There is also a list of which parts were removed or integrated into other parts.